Radioactive waste materials and synthetic rock precursor may be poured into a compressible, bellows-type canister which is closed and then subjected to hot uniaxial pressing such as described in our U.S. patent application Ser. No. 524,841 now U.S. Pat. No. 4,645,624, assigned to the assignee of the present application.
A known alternative to the present applicants' hot uniaxial pressing process is a hot isostatic processing in which the particulate waste material and synthetic rock forming material is placed in a metal container which needs to be evacuated and completely sealed. This metal container is then subjected to high temperatures with a very high surrounding gas pressure to cause compaction of the material within the canister as it forms a synthetic rock. Thus the canister is supported on all sides by the gas pressure and the very nature of the process is such that any gaseous material within the container must be retained therein. When a canister is filled with the particulate mixture (for forming the synthetic rock incorporating radioactive waste) even if a high filling density is achieved there will be a considerable quanitity of gas in the interstices of the mixture, unless the gas is completely evacuated, a time consuming and complex process in an active cell.